1. Field of the Invention
The present invention relates to radiography and more particularly to an examination system and method utilizing ionizing radiation and a flexible, miniature radiation detector probe.
2. Description of the Related Art
X-radiography is useful in many areas of non-destructive testing especially when voids, cracks, and corrosion in assembled structures are of interest (1). Filmless detectors have increased the throughput, eased storage problems, and reduced radiation exposure hazards while eliminating the costs and hazardous processing waste due to film-based x-ray systems. Most x-radiography systems use a point source and high resolution detector array such as an x-ray image intensifier coupled to camera tubes (2) or scintillators coupled to charge coupled devices (CCDs) (3). Due to the relatively large size of these detectors, they are difficult, if not impossible, to use for some in-situ appilications. There is clearly a need for an examination system utilizing compact, i.e., miniature, radiation detectors for areas having limited access.
When an examination system is employed within enclosures containing radioactive, volatile, flammable, or corrosive materials, or enclosures maintained at high temperatures, expensive efforts are required to mitigate these damaging environments before introducing the examination probe and/or x-ray source. There is clearly a need for an examination system utilizing environment-resistant components. There is also a need for an examination system in which the electrical components are remote from the hazardous area being examined to eliminate the possibility of an ignition of materials.
Hospitals today are switching to filmless radiography due to reduced budgets, strict radiation exposure policies, environmental concerns, and the need for convenient storage and fast transmission of information. By using detectors much more sensitive to x-rays than film, the dose received by a patient can be reduced by a factor of ten or even more (4). Also, by using purely electronic detectors the costs and hazardous waste due to film and its associated processing are eliminated. The electronic images generated can be stored in a much more compact manner and transmitted anywhere in the world in minutes. One of the main problems in the conversion to electronic imaging, however, is in trying to achieve the same spatial resolution as film. Some of the techniques currently used or under development are arrays of photodiode sensors coupled to phosphor screens (5), CCDs coupled to scintillators with a fiber optic taper (6), and x-ray image intensifiers coupled to camera tubes (7). Many of these systems suffer from cost and/or resolution and contrast sensitivity problems. They, along with film, are also prone to a degradation of resolution due to scattered x-rays from the patient, thus producing a "fuzzy" picture. There is a need for an examination system utilizing simple, inexpensive detectors to produce clear, nearly scatter free and high resolution real-time images for use in the medical and dental fields.
The present invention is an examination system and method, based on the Reverse Geometry x-Ray.RTM. (RGX.RTM.)* radiography technique, which has been optimized to solve the aforementioned problems. The reverse geometry x-radiography technique "reverses" the size and location of the x-ray source and detector of the conventional x-radiography technique. With the RGX.RTM. system the object to be examined is placed next to a large raster scanning x-ray tube anode with a "point" detector located anywhere from a few centimeters to a meter away (see FIG. 1). The x-rays are produced when a microfocused beam of electrons strikes the high Z target/window anode. Magnetic deflection coils sweep the electron beam in a raster pattern across the broad anode plate producing a moving point x-ray source. A computer correlates the positions of the x-ray beam to pixels on a cathode ray tube screen with the output of the detector at each point giving a transmitted x-ray intensity value to the pixel. FNT *Reverse Geometry X-ray.RTM. and RGX.RTM. are registered trademarks of Digiray Corporation, 2239 Omega Road, San Ramon, Calif. 94583.
Real time stereoscopic images can be obtained with the RGX.RTM. system due to its fast scanning rate (approximately 0.25 seconds for 512.times.512 pixels, approximately 1 second for 1024.times.1024 pixels) and ability to read two point detectors simultaneously. The current system has a resolution of greater than 7 lp/mm and a contrast sensitivity of about 0.2% for thin, low density specimens (8). The use of a single channel point detector as the imaging element allows the use of small detector probes which can be placed inside objects to produce images of one area without interference from another area as would occur if the x-rays traversed the whole object prior to detection. The remoteness and small size of the detector eliminates detection of scattered x-rays thus improving resolution and removing "fuzziness" from the image.
The references cited above and throughout the following specification are listed in Appendix I of the application; they are incorporated by reference herein. Additional publications which are incorporated by reference herein are listed in Appendix II.